EU referendum: London will be stronger if the UK remains as a semi-detached member of the club

Any freedom gained by Brexit will come at the expense of opportunity and London will bear the brunt if Britain votes to leave.

London will be stronger if the UK remains as a semi-detached but full member of the club, as negotiated by Prime Minister David Cameron in his reform deal. London has flourished by being open to Europe for 43 years since joining. London has made itself the headquarters for 40 per cent of Europe's top companies and 60 per cent of global non-European firms have chosen London as their base within the bloc.

Finance

The City is the world's biggest financial centre because US banks choose London as an English-speaking city with the right to sell financial services freely across the entire EU.

This right is secure if we stay in, but would be lost if we left. Paris and Frankfurt are set to gain at London's expense if all the banks based in London lose passporting of financial services and euro clearing rights following Brexit.

Housing

Tackling London's housing crisis remains the leading issue in London's Mayoral election. All the leading Mayoral candidates have seized on the idea that building on surplus public land is the key to supply.

However, Brexit would put delivery of those new homes at risk as today as we rely so heavily on the skills of EU workers in the construction industry and at least 20 per cent of the materials are supplied from the continent.

Technology

Technology is London's fastest growing industry and the talent shortage is its single greatest threat. EU migrants are net contributors to the economy and bring many highly valued skills to the British work force. A survey of London's tech sector showed overwhelmingly that it will be harder to reach EU customers and to employ people from EU member states if Britain is outside the EU.

EU membership also means our universities can benefit from Horizon 2020 grants for medical and scientific research on an international collaborative basis - and London institutions have persistently received a large and disproportionate share of that fund.

Security

London will be safer inside the EU in a dangerous and increasingly unstable world. Cross-border intelligence sharing, facilitated by Europol and Eurojust, expedites bringing criminals and terrorists to justice. Our domestic security is boosted by EU instruments like the European Arrest Warrant and Passenger Name Record databases.

When crimes do take place, the European Arrest Warrant allows us to send suspects back to face justice in other parts of the EU and swiftly bring those back who might escape abroad. This was exactly what happened when Hussain Osman, who attempted to blow up the Tube in July 2005, fled to Italy. Instead of lengthy extradition procedures, which used to take up to 18 months, we were able to bring him back within a couple of weeks. As an EU member, Britain has the right to opt into the Schengen top security database to check the names of people crossing its border.

A popular fiction pedalled by the Out campaign claims the UK's EU membership prohibits us from barring access to Britain for suspected criminals and terrorists. This is simply not true. Over 6,000 non-British EU citizens were turned away by UKBA in the last six years on the grounds of their potential risk to public safety, further strengthened by Cameron's recent deal.

Britain has joined the EU-wide Prüm convention for sharing fingerprints and DNA, which Britain will fully implement next year - unless we leave the EU - helps to catch criminals faster. It takes an average of 143 days for a DNA match to be returned through the Interpol process, but under Prüm it will be 15 minutes.

Those advocating that we leave the EU have not been able to say if we could negotiate equivalent security arrangements with member states from outside. Turning our back on the EU would undermine our safety in the future and puts at risk the intelligence-sharing and international cooperation that our law enforcement agencies rely on.

The future is Green(land)?

Brexit is a risky leap into the dark. There is clearly no cast-iron Brexit economic plan by Leave campaigners and the UK cannot dictate its exit terms. We face a tricky separation, followed by years of uncertainty before a final divorce, as 27 EU leaders deliberate and vote on the UK's exit deal.

Greenland, the only precedent, is the size of Croydon and has one industry - fish. It took two and a half years to negotiate one minor exit treaty. The UK has in effect over two hundred exit treaties to negotiate.

This includes unscrambling over 50 EU Free Trade Agreements which will require renegotiation of bilateral trade deals as replacements, and there is no guarantee that third countries have any appetite to do so in a hurry.

Could London be demoted to England's capital city?

London is the greatest global city on earth, a magnet for tourism and talent from overseas, but its status as the capital city of a United Kingdom is bound to change following Brexit.

A constitutional crisis could ensue that would break up the UK if England votes Out and Scotland votes to stay. Similarly, how will Northern Ireland and its Catholic population cope with a new customs border with the south?